It would be better to have a buffer tank so that you can supply heat at different times, while just running the heat pump at night. You may find that on sunny days that some floors are too hot if they are heated all night.

Forgive my scepticism on just using an ASHP, I'd suspect that the only way to keep the running costs reasonable, (and bearing in mind the unlikely situation that you could get away with only using "economy" electricity), would be to add something like a woodburning stove for the coldest weather, and solar hot water for domestic hot water during the summer months -quite apart from wanting "back up" for that time you lose power supplies when it's freezing cold....

Hi there the Nordics are a new product from Daikin in the UK, (they may be more established on the continent though), they look good because the outputs available at lower ambients are greater giving you more coverage, without a big drop off in efficiency when compared with their standard model. It is currently about 4-6 months away from MCS accreditation in the UK but I don't know whether this would apply where you are.

You say you have UFH already, but if this was designed for higher flow temps and a delta t different to that of the Daikin (5 degrees) you may want to check that it will provide enough heat from the floor with a lower flow temp and use as buffer to avoid destabilising the unit. If the manifolds have blending valves we would recommend removing them too.

The company also fitted an inline KwH meter so I can get an accurate reading of the ASHP power usage

Only in 4 days now but I know from past costs that the ASHP is heating my hot water at 50% of what oil cost, I know this will change as the weather gets colder but is a good sign

On the first night after installation I turned up all my room stats (11). Next morning the house was very warm and had a tank of hot water, all on Economy 7 ----- COST --10 units at 6.08p per unit, again I know this will change as the colder weather hits but it still looks promising

I am keeping an accurate log of costs etc and will try and update here on a regular basis

I have the original oil boiler still connected as backup and have a 8Kw Stovax woodburner in the living room for the

I will be very interested in seeing how the system works over the winter. I was pleased my main source of heating was a GSHP rather than an ASHP last December and I had a WBS amongst other things as a backup. A lot I think depends on how well the system is designed, in the UK ASHPs normally perform well below the manufactures specification in terms of COP. Curiously in discussion with NAREC the other day there is a new Netherlands study in which the actual performance of ASHPs seems to be better than published COPs. Will try to get a link to the NL study if anyone is interested.

The company also fitted an inline KwH meter so I can get an accurate reading of the ASHP power usage

Only in 4 days now but I know from past costs that the ASHP is heating my hot water at 50% of what oil cost, I know this will change as the weather gets colder but is a good sign

On the first night after installation I turned up all my room stats (11). Next morning the house was very warm and had a tank of hot water, all on Economy 7 ----- COST --10 units at 6.08p per unit, again I know this will change as the colder weather hits but it still looks promising

I am keeping an accurate log of costs etc and will try and update here on a regular basis

I have the original oil boiler still connected as backup and have a 8Kw Stovax woodburner in the living room for the

-15 C days

The Bassman

Great to hear all is well :)

I think what a lot of people forget is that a well designed ASHP system keeps your house at a nice warm even temp with loads of hot water for sod all running costs. If it is a bit dearer in winter so what... 95% of time its buttons to run.

So many oil/LPG users I know spend way way more and hardly heat their houses at all wackoold Indeed I was in a friends modern house, oil boiler, recently and it 14c, to expensive to turn on until winter :winter Our house was like that last year but no more exhappy:

Martinwell yes, but there is nothing wrong with ASHP technology it is just so often in the UK that systems are badly designed and implemented. Why do the work so much better in Scandinavia or indeed continental Europe? A well implemented ASHP system can perform well and should do so in Northern Ireland, though if last December is going to be the norm then it will test any system to the limit

We installed an ASHP to heat a converted garage almost a year ago now, the COP is just under 3 averaged out through the year, that includes a couple of weeks when it didn't do much in the worst of the snow. The customer uses an oil filled rad as backup for those periods, the consumption of which is added to the consumption of the heat pump to calculate the COP. The essential factor is providing a big enough heat exchanger outside and to place it in a position where it can make use of any sun and get an adequate flow of air. So many of them have the exchanger placed behind the bin shed or whatever they're bound to struggle.

"Why do the work so much better in Scandinavia or indeed continental Europe?" - my understanding is that the innate "sogginess" of the UK climate really doesn't help midwinter performance of an ASHP - and as has been pointed out, they're often incredibly badly chosen/sized/fitted in this country, and to make the most of the low-grade heat available, you really need underfloor heating - they really aren't the "straight swap for a conventional boiler" for which they are often touted! Certainly the technology "works", but in my experience they are often oversold on their "COP", and have come across all sorts of wildly inaccurate claims from their vendorsIn practical terms, you'll need another form of heating for the depths of winter, and to tide you over through power cuts, add to that the reported reliability problems, and the fact a lot of people are ripping the things out as they've proved ineffective/too expensive to run, and the "wisdom" of overloading an already creaking grid with the things I remain sceptical as to their widespread usefulness.... I certainly can't see any sense in using them where mains gas is available

"Why do the work so much better in Scandinavia or indeed continental Europe?" - my understanding is that the innate "sogginess" of the UK climate really doesn't help midwinter performance of an ASHP - and as has been pointed out, they're often incredibly badly chosen/sized/fitted in this country, and to make the most of the low-grade heat available, you really need underfloor heating - they really aren't the "straight swap for a conventional boiler" for which they are often touted! Certainly the technology "works", but in my experience they are often oversold on their "COP", and have come across all sorts of wildly inaccurate claims from their vendorsIn practical terms, you'll need another form of heating for the depths of winter, and to tide you over through power cuts, add to that the reported reliability problems, and the fact a lot of people are ripping the things out as they've proved ineffective/too expensive to run, and the "wisdom" of overloading an already creaking grid with the things I remain sceptical as to their widespread usefulness.... I certainly can't see any sense in using them where mains gas is available

MartinI don’t disagree with regards to much of what you say. I’m not sure about the sogginess of the UK being a killer. It would be interesting to compare ASHPs Norway and Sweden as parts of Norway e.g. Bergen are famously soggy. You are absolutely correct regarding “badly chosen/sized/fitted” and the need for UHF. They are absolutely NOT suitable for a direct boiler replacement.There is nothing however intrinsically wrong with ASHP technology, unlike small roof mounted wind turbines or mirrored sunboxes! My own ASHP (used for hot water only) is used to back up the Navitron vacuum tube system. This has run over the summer for on average a bit less than 1 unit of E7 electricity per day even with MrsBs voracious use of hot water! Granted that this is as much a tribute to the Navi tubes as to the ASHP system.

A flow chart might be useful...

Do you have mains gas?Unless your ASHP/GSHP system is very well designed you are unlikely to save any money on running costs. The capital cost however is likely to be far higher than a conventional boiler/central heating system. Under almost no circumstances therefore is a heat pump system a good idea.No Mains Gas.Do you have underfloor heating and a building with a large thermal mass and long time constant? Then it is worth looking into heat pumps....

Your figures concern me, about the13/10 you appear to be using >60kWh of electricity for your heat pump per day, this would imply a heat input to your house of about 180kWh/day at a COP of 3. If we take off say 15kWh for DHW this would leave about 165kWh/day.You have a "well insulated" 180m2 house - I would expect to heat it in January with about 70-80kWh/day never mind a mild October so I think either you have a problem with your heat pump or insulation (including draughtproofing)

Bottom graph shows daily costs for the first 31 days I have had the ASHP running

This is 75% of the house at 22C and keeping the 220litre DHW tank filled

House as mentioned before is detached 185sqm bungalow with UFH all over, I have the system running 19hrs a day 2am to 9pm - the reason being that the Economy 7 kicks in at the moment (until the hour change) at 2am and I want to make sure I get the full benefit of this by letting the house cool from 9pm.

I will be experimenting with these times to get the most economic, but this seems ok at present - I don't want to heat the house from 9pm and then the ASHP turn off when the cheap rate kicks in if you see my logic!!

I will try and get the temps for that period if possible and add them to the graphs

To the last post - these high periods were when we had to have the DHW tank filled a couple of extra times due to a heavy use of hot water

Big differences from day to day 15 kW to 34kW is that just caused by changes in outside temperature or is there an immersion in the system distorting the usage? I presume at this time of the year you would still be getting a COP of 3 so it would mean 102 kWh output which is a lot of heat.

If you can set higher room temperatures at off peak times you should be able to force the system to do more heating at the low rate. You just need to set the thermostats to a lower temperature outside the economy 7 hours. It won't mean that the rooms will be cold just that the heat will be from stored heat in the floor only. This should also improve efficiency by keeping the compressor running constantly but for a much shorter period.

Would you need historic energy use to calculate COP now that you have an ASHP? In other words you normally use x amount of energy and now you are using y to power the ASHP - I take it there is no display showing power in and power out.

Just had a nice surprise - I have been awarded a grant of £1860 from PowerNI

This is for new installs of Renewable energy equipment and is to help with the initial purchase costs until the RHI is implemented in Northern Ireland. This scheme is only available for 3 mths until end of December. Have to have a photo in local papers for publicity of the scheme.

ASHP is running this month at an average of 26 KwH per 24hrs at present, this includes 3 nights of severe frost and 0c mornings when the dogs water bowls were frozen over!!

I am now taken KwH readings at the change over times from peak to off peak electricity to get accurate figures.

thanks for keeping us informed. I've been meaning to instrument my GSHP system for some time.

At the risk of sounding pedantic you should use kWh rather than KwH. K is a unit of temperature (Kelvin), H is a unit of inductance (Henry). I have no idea what lower case w stands for - it is not normally used in the SI system.

Hi Bassman, did your installer give you the breakdown of energy useage from the Daikin sim, it would be interesting to see how you are performing against their software prediction. We have 2 that we are monitoring at present and both are ahead of the Dec prediction despite 1 of them not being a fully finished project.

Also have you considered the impact of the lower COPs available overnight due to lower ambients. Its not unusual to set back flow or air temps overnight to combat this and also to avoid hot water charging during the night, we usually set the hot water to constant demand to avoid long spells of hot water heating that detract from heating the house. This generally means that the cylinder is back to setpoint after its last use and not charging through the coldest period. If you are not using set back at the moment, don't reduce by more than 2 degrees otherwise the recovery load is to great.

As yet we have not empirically assessed the cost of either option but might be something to try.

Hi, was just wondering how noisy the outdoor units are in real terms. We lived in Oz until for 5 yrs and lived with the need for air conditioners from time to time, I think they are essentially the same but in reverse and the units look the same . The fans in them can make quite a drone which never bothered us much but at night could be annoying, how do you find your system, I guess that is one of the factors that is a compromise when placing the outdoor parts, best position - least noise. In Oz you have to replace your old emmersion water heater with an ashp standalone unit when your old one packs up. How well they work on a + 40c day I don't know, but then cold shower is what you need anyway!

To answer the last two posts, no I was not given a breakdown of the energy usage just a yearly estimate that seemed satisfactory at the time

In saying this I am happy, at present my energy usage from October is half (cost wise) of what a work collegue is using in oil and we used very similar amounts of oil over the last 5 years

Regarding noise, unit is very quite unless it is getting to the point of going into defrost mode and is finding air hard to get! Overall you would not know it was running

Here is my latest graph showing December figures for my ASHP - As can be seen the frosty and icy days and nights mid December saw a heavy increase in power input. Nevertheless I am still saving around 40% on running costs compared to oil and I still have to get my RHI payments

Hello Bassman, Its wonderful to see that data - thanks very much for posting it. Thinking about JonG's post but thinking in reverse if that makes sense. Your peak units cost over twice your cheap units. Even considering a lower COP at night is it possible it may be cheaper to slightly over heat the home on cheap units. This would mean less peak units. Whether this would save money overall is not an easy thing to work out. But with the data you have you could compare any new heating scheme with the old data. Also with a 16 kW ASHP it would need to run this for 3 hours on some cold days. Could all of this be on cheap units ? I suppose it depends on how well your home holds in the heat over time.

Hi Bassman, just out of interest here are the average daily consumption figures for the 4 that we have monitored at the moment for December:

Daikin 16kw Nordic: 49 226 sqm property

Twin 16kw Daikin Standard Low temps: 73 700 sqm Property

NIBE 11 kw Fighter: 21 128 sqm property

Grant Aerona: 19 (Heating only) 118 sqm property

I can't quite calculate what your average total usage per day is from the graphs, but Dec where we are was a good representative month in that it was only plus 1 degree above the 30 year normative temperatures. The 2 Daikins were circa 36% better than what the December month prediction from their software would suggest, NIBE's software does not offer a month by month prediction and Grant don't have any software.

We would love to record cop but quite problematic and expensive to do and customers are more interested in cost which we can do simply with a meter.

The meters on the daikins record all consumption including extra circulators controls etc. We set them up to only use immersion for pasteurisation to keep dhw costs down and aim for a setpoint of 47-48 degrees.

The nibe has a meter on immersion, heat pump and back up but only heat pump data on here, immersion is for pasteurisation only and backup has not kicked in.

Grant is a long story only worth telling if someone is considering one.

Station house are your figures purely for the heat pump or domestic consumption too?

Nordic is not mcs yet but customer wanted the low coverage it offers.

Batman if you have your location, heat loss and hi and Lo flow temps I can model your system through the daikin software and confirm monthly consumption.

We would love to record cop but quite problematic and expensive to do and customers are more interested in cost which we can do simply with a meter.

The meters on the daikins record all consumption including extra circulators controls etc. We set them up to only use immersion for pasteurisation to keep dhw costs down and aim for a setpoint of 47-48 degrees.

The nibe has a meter on immersion, heat pump and back up but only heat pump data on here, immersion is for pasteurisation only and backup has not kicked in.

Grant is a long story only worth telling if someone is considering one.

Station house are your figures purely for the heat pump or domestic consumption too?

Nordic is not mcs yet but customer wanted the low coverage it offers.

Batman if you have your location, heat loss and hi and Lo flow temps I can model your system through the daikin software and confirm monthly consumption.

Apologies Bassman, too late and too many projects on the go! The offer still stands though even if you aren't quite as heroic as I might have suggested.

Just some more background on the jobs listed before, now I have some more time.

The Nordic is on a retrofit with an extension, a mix of UFH in screed and pug with tiles and oversized rads. We are expecting it to improve because about a third of the ground floor is yet to be insulated, some of the UFH has not been laid and some of the existing UFH is exposed.

The twin Daikins are on a new build with good insulation levels and UFH throughout in screed. The design of the UFH was not ideal though with a max temp of 43 degrees at minus 3, we design for 35 degrees with 100 mm centres and 80m max loop lengths. Floor coverings are tiles and carpet and although the customer swears blind they are less than 1.5 tog I am not convinced!

Both are into buffers and use sampling to control the buffer temp.

The NIBE should improve too, we discovered last week that the 3 port had failed and prior to this it had intermittently been failing during hot water production, spiking the floor temps and overheating the buffer. Valve is being changed out on Friday. This is a barn renovation with our own design of UFH in a screed with tile, but there are a few too many rugs in the main living area that I flagged to the customer last week.

Thanks for the link Sam I'll have a look at those, it looks like it fits in line on the return?

I'm considering an ASHP to supplement the oil boiler, but without a Buffer Vessel. Am I wasting my time / money?

Boiler and DHWC are not two years old, and the DHWC is a triple coil affair, with solar in the bottom, oil on the top and soon to have a WBS in the middle. CH via radiators & 3.6kW PV on the roof so "free" electricity (until smart meters that double as Export meters spoil the party!!!). House is empty most weekdays, but I have a wife that feels the cold - I'm in shorts & T-shirts, she's in jumpers & fleeces!The ASHP would only run if it's CoP was sufficiently high otherwise the oil boiler would cut in. I haven't got anywhere to put even a couple of hundred litre buffer vessel, so the ASHP would be directly feeding the CH - low grade heat to radiators.

So I'm wondering, if there is good sun for the PV to be working and run the ASHP for free (ish), the chances are the demand for heat won't be that high. Otherwise the CoP would have dropped off and the oil boiler will be utilised...

Hopefully you see my dilemma and some bright spark can put me right!

Through a work contact I can get a good deal on a Grant Aerona, but now concerned about what Jon G was alluding to:-

SB, you need to think about the load first i.e. the heat loss, which is now very stringently controlled via the new standards and if you are going bivalent there has to be a common control strategy for the oil integration which does limit your choices to a degree in terms of unit and there are now also guidelines about how the bivalency is set up. e.g does the ASHP drop out at equilibrium point or is it supported by the oil boiler. If the latter you would need to consider a buffer to deal with defrost issues, to provide you with a "hot" reservoir if the energy in the house is low due to reduced setpoints because you are not there.

If you are thinking of having the heat pump cover marginal loads above around 6 degrees defrost is unlikely to be an issue so a buffer would not strictly be necessary for defrost. However you have to ensure that you get the flow rate for the unit and minimum system volume at all times, any zones, TRV's and so on could cause an issue as would 10mm circs. Make sure a flow meter is installed and delta t's are rigorously checked at commissioning. This would also affect your decision regarding the unit, for example Daikin's need a 5 degree delta T which is difficult to hit on rads, Mitsubishis work to a 10 degree delta but cannot be integrated into a bivalent strategy yet. Swedish units like NIBE and Danfoss are easy to bivalent but would require a buffer. We have creatively managed to accommodate buffers before, using out buildings, lofts, bespoke outside insulated enclosures etc.

You will also need to think about rad sizing to maximise efficiency from the HP. Also the cylinder does not have a separate coil for the HP so I am guessing it would be heat only, if not the coil needs to be sized to suit the low flow temp off the HP.

The Grant was commissioned and designed by them using various components from different manufacturers. It is a fixed speed unit which can have up to a max of 6 starts an hour which is huge variance from common thinking which generally targets no more than 3. This wear and efficiency issue cannot easily be resolved because the on off is dictated by a LV switch from a standard stat, as opposed to a thermistor which would usually be employed with a buffer. The programmer is restrictive in terms of user settings and manipulation for site specific conditions, including recruitment of the immersion and setting the bivalent point. We picked up an Aerona after it had been installed and left unfinished by the original installers. So far we have been unable to get the cylinder above 35 degrees, despite the fact it is a Grant designed HP cylinder with a solar coil that we have also used to try and increase the heat transfer.

Grant make very good oil boilers but the Aerona has some classic design faults that they openly admit were originally designed in to suit the UK market (no buffers), an inverter without a buffer can be problematic but a fixed speed ASHP without a buffer is not a good idea at all. Their cylinder routes the primary coil through the cylinder and back-up so that the return leaves at the same height as the flow, this has the effect of driving up the return temps as it accumulates heat from the hottest part of the cylinder and switches out the heat pump on the return sensor before the cylinder stat is satisfied. The base design is for an S-plan layout (2-2ports) but this is not a hot water priority set up so when the hot water valve energises the space heating valve stays open. the HP ramps flow temp and feeds the house and cylinder simultaneously, overheating the house and under heating the cylinder. Apparently this was because it was too complicated for plumbers to set up the required relays to shut the house valve when the hot water energises. Their solution is a packaged £200 relay switch to bring the cylinder immersion on at around 40 degrees to hit 60.

JG - thanks for the information (and the heads-up on the Aerona) although I would have to say I had to read it several times to try and understand!

Whether it is either / or for the heat source, I hadn't really considered. My initial thought was that as the CoP dropped off, the oil boiler would take over, but if they can be used in conjunction to get the most efficient solution, happy days.Although you have now got me thinking, could you have a floating bivalent point? As the price of oil & electricity fluctuates, so will the preference as to which would be the less expensive heating option.

I think that you are saying that the ASHP needs to maintain a constant flow rate and that zones etc can upset the balance. As we have 18 rads over 2 zones, it strikes me we would be on a hiding to nothing as the volume is going to be variable. As an aside, the existing system is currently open vent, does this mater? If it is an issue, could the ASHP be integrated via an PHE? That way the systems are split, the ASHP can be pressurised as required and the volume of fluid in the ASHP circuit will be constant...

As for the radiator sizing issue, I was figuring that if the external temperature was high enough for the CoP of the ASHP to be acceptable, the heat demand would not be overly high and a slower rate of heating would be acceptable. Or is this naive?I have to admit, I don't quite understand what you mean by

Quote

Daikin's need a 5 degree delta T which is difficult to hit on rads, Mitsubishi's work to a 10 degree delta...

It was my intention to leave the DHW running off the solar / WBS / oil boiler as ASHP's struggle to heat to 60'.

From what you appear to be saying about the Aerona, what I save on the unit, I will loose out on performance.

Thanks for taking the time to reply, and hopefully I have understood what you are saying.

As far as I know the only product that calculates the fluctuation in utility prices and chooses the best option based on user inputs, is the Gloworm heat pump and hydrobox module. This would be worth a look in your particular instance, we actually helped with some of the design parameters on this product but have to confess to never actually having fitted one becuase we tend to always aim for 100% coverage from the HP to ensure any RHI is payable, but when we saw the pre-production mock ups it did look good and very clever in the way that it selected the most appropriate heat source for the property at any given set of parameters. It did also have the HE you refer to to match it with an existing system, but from memory both sides have to be pressurised. If you make contact with your local Gloworm rep via a merchant I am sure they will provide more information on it.

Where are you geographically by the way?

The zone and flow rate aspect was another reason why we were shy of the Gloworm product, 18 rads and 2 zones is fine, it is multiple floor zones that cause the most headaches, where each room is a separate zone. We always use a buffer to guarantee flow rate and provide for defrost, which mitigates to an extent, what is downstream anyway.

In terms of the radiators, because the unit should weather compensate, whilst the demand is lower at higher outdoor ambients, the flow temp will reduce and therefore larger emitters are still needed. If you really can't or don't want to upsize the rads a high temp may be worth looking at, but price and complexity increase and efficiency decreases.

The delta T is the difference in temperature, in this case between flow and return. the heat exchanger in each heat pump is designed with different optimal performance levels based on flow rate and delta T which are a function of each other. This is another reason why we use buffers and something to consider if you end up using a PHE, due to the need to match its performance with that of the heat pump in terms of heat transfer, flow rate and delta t.

In terms of hot water, we tend to always target around 48 degrees store temp to avoid daily immersion usage and then pasteurise periodically. This is usually within the capacity of most units.

The overriding point about heat pump systems is that simplest is best, bivalent can work but you will need to source a good installer to get the best set-up and ensure that the HP is designed to be easily integrated and controlled.

If you can make a stab at your heat loss and provide some insight to your insulation levels I might be able to be more accurate about HP specifics.

The Glowworm looks like a possible solution, but it does seem to imply that the heating circuit would need to be pressurised. I will follow that one up.

You imply that the RHI (if they get it sorted) is only likely to be payable on stand alone systems. A bivalent system would not qualify. Am I reading this right?

Some of the rads will need changing in the not too distant, but wasn't planning on doing them all in one go. According to the Myson website, they would need upgrading by a factor of 2.4. When you consider that we have 18 of them, and most are 1600mm twin panels, that won't be cheap! That and the fact that we aren't going to have a lot of wall space left!!! I would love to go underfloor, but that is another expense we can't stretch too.

The property is in the Maidstone / Sittingbourne area of Kent. Cavity wall insulation was done last year and we have masses of loft insulation. 217m2 of floor space with a Grant Oil boiler rated at 19kw. Double glazed throughout, but they haven't got the best U rating in the world. Solar Thermal & PV already on the roof. Built in 1972 by the church, to a good standard. (Square, straight walls, solidly done.)

Thanks for the explanation on delta T. I was guessing that is what you meant, but thanks for confirming it.

I have also been reading the EST Heat Pump Field Trial, which basically says that the success of an installation is primarily down to the way it is installed and the commissioning. It also says that you should keep it simple, which it seems to me I am endeavouring to do anything but!

It does seem that I have managed to hi-jack someone elses post. Being a Newbie, if this is bad form, perhaps one of the Moderators could let me know and I will start a new one.

No problem at all. We are in the NW so can't help physically I am afraid. If you have a look at this link http://www.microgenerationcertification.org/installers/installers/decc-heat-pump-training-road-show there is a raft of information on sizing and on the right hand side a Heat Emitter Guide that you can use to ascertain whether the existing radiators would:

a. Work with a heat pump without up-sizing albeit at a lower COPb. Confirm up-sizing factors and impact on COP

We use K3 rads quite a lot now which are triple panel triple convector, so footprint is smaller but depth greater.

At 217sqm and the insulation values you describe heat loss would be in the region of 11kw very roughly. This should be coverable on a Daikin Altherma LT or Nordic or a Danfoss DHP-AQ, both can be set up for bivalency. Not sure what the outputs are on the Gloworms.

One of the best references I have on the subject is John Cantor's book which is a worthwhile investment if you are serious about the project. http://www.heatpumps.co.uk/

In terms of the RHI, basically who knows! We have always worked on the premise that it will not permit bivalent operation, despite the fact that it makes excellent sense in some instances, also the latest MCS guidelines cover bivalency in some depth so maybe they are relenting to a degree. I know Gloworm were petitioning hard to justify their R&D spend.

Some of the Grants can be pressurised or open vented, depending on when they were manufactured, be worth a call to them to check.